Marinoquinolones and Marinobactoic Acid: Antimicrobial and Cytotoxic ortho -Dialkylbenzene-Class Metabolites Produced by a Marine Obligate Gammaproteobacterium of the Genus Marinobacterium .

Chemical investigation of the culture extract of a marine obligate proteobacterium, Marinobacterium sp. C17-8, isolated from scleractinian coral Euphyllia sp., led to the discovery of three new o -dialkylbenzene-class metabolites, designated marinoquinolones A ( 1 ) and B ( 2 ) and marinobactoic acid ( 3 ). Spectroscopic analysis using MS and NMR revealed the structures of 1 and 2 to be 4-quinolones with an o -dialkylbenzene-containing side chain at C3 and 3 to be a fatty acid bearing an o -dialkylbenzene substructure. The 4-quinolone form of 1 and 2 was unequivocally determined by comparison of the 1 H, 13 C, and 15 N chemical shifts of 1 with those predicted for 2-methyl-4-quinolone A and its tautomer 2-methyl-4-quinolinol B by quantum chemical calculation. Compound 1 was proven to be racemic by X-ray crystallographic analysis and chiral-phase HPLC analysis of its chemical degradation product. Compounds 1 - 3 exhibited antimicrobial activity against bacteria and filamentous fungi at MIC of 6.3-50 μg/mL. In addition, all compounds showed cytotoxicity against P388 murine leukemia cells at micromolar ranges.